okay, I'll bite. Anyone for Mag Stim?

john f andrews ece jfa0522 at hertz.njit.edu
Tue Aug 6 13:08:55 EST 1991

In article <22618 at duke.cs.duke.edu> tbd at neuro.duke.edu (Tristan Davies) writes:
>In article <1991Aug5.134013.19105 at njitgw.njit.edu> jfa0522 at hertz.njit.edu (john f andrews ece) writes:
>>I have become involved in an experimental project involving transcranial
>>magnetic stimulation of the motor cortex.
>>Naturally, this is a frontier area, and is not well understood as of yet. 
>>Has anyone any information regarding this?
...stuff deleted...
>I think that "cortical columns," whatever they are, are smaller than
>a square cm.  Ocular dominance columns in visual cortex, which is as
>close as anyone's come to defining a cortical column I think, are on the
>order of 1 mm in width.  If you choose to define a "column" as an
>orientation-selective piece of brain, then the column gets even smaller,
>maybe even 0.1 mm square.  Tread carefully on such thin ice...

Thanks you for pointing that out. I tend to take things visually, I guess
due to my engineering training...if someone says collumns and draws a 
diagram, I think collumns.... I will investigate before treading any further...

more deleted, even tho intresting, to please sysadmins...
>This *is* a clever idea, seeing as how it seems to stimulate neurons to fire.
>It might even have some clinical possibilities...how about detecting and
>thwarting seizures???

There has been noted a functional organization of the cortex, as ellicited
through mag stim mapping. There has recently been talk of a plasticity of
the motor cortex, with the functional "mapping" reorganizing post trauma
. Should mag stim prove effective w/r to selectivity, as a means of
inducing firing, perhaps it could aid in detection/elucidation of said
organization? There are definitely clinical uses... but again we have to
evaluate the technology.

>In the world of experimental neuroscience, though, I can think of a problem.
>If you want to understand in any detail how the firing of neurons generates
>a behavior, I think it's necessary to know in detail where the site of
>stimulation was.  Recording electrodes leave tracks, which can help you
>find the recording site, and if you record through a pipette, you can then
>eject markers (e.g. HRP) to mark the recording site with a level of resolution
>and certainty that don't seem to be possible with transcranial stimulation.

Ay, there's the rub. What is the actual field? What distortion occurs (if
any) in the tissues? What is the field gradient in the tissue, and is it steep
enough to selectively stimulate? Good questions... key questions.

Am I wrong to believe that if "recording electrodes leave tracks", then 
damage is being done?

>Given the recent evidence linking electromagnetic fields to some diseases,
>I wonder (as you do) how non-invasive this really is...
>Of course, X-rays cause cancer, so I guess nothing's perfect.
>Tristan Davies
>e-mail: tbd at neuro.duke.edu
>Department of Neurobiology, Duke University Medical Center
>"grblb blabt unt mipt speeb!! oot piffoo blaboo..." -- Opus

A widely misunderstood and little understood field. May I ask what recent
evidence has linked fields to cancer? I haven't seen any yet.

I guess there must always be comparisons.... Mag Stim is a single pulse,
high field strength. MRI is high field, long exposure, and much more
"radiation" due to concurrent rf and dc fields. Electric stim is
higher current, and if energy is used as a measure of potential harmfulness,
mag stim is less dangerous than many, many daily exposures we endure. I
don't think we could get volunteers to sit before an x-ray machine and get
x-ray'ed.... I'd like to be sure mag stim is no way near that.


john f andrews                SYSOP           The Biomedical Engineering BBS
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